High quality capacitors are required in the design of mixed signal and RF circuits to compensate for the limited quality of on-chip inductors in resonators or to provide decoupling (to prevent RF coupling on power or ground lines). Metal-on-metal (MOM) capacitors are often used and these are built using standard IC-interconnect layers. These capacitors may also be referred to as metal-metal comb or fringing capacitors.
Current capacitor designs include Manhattan-style capacitors with all conduction paths at right angles, as shown in FIG. 1, which comprise woven fingers of metal 101 in each layer 102, 103 and Vertical Parallel Plate (VPP) capacitors. Fractal capacitors have also been proposed which randomize the orientation and shorten the length of the current paths in the device.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known metal-on-metal capacitors.